Melanoma is the most dangerous type of skin cancer. With about 48,000 melanoma-related deaths reported worldwide every year, it is the leading cause of death from skin disease. However, while repeated exposure to UV radiation from sunlight is known to increase the risks of developing all skin cancers by mutating the cellular DNA, currently known UVB-signature mutations from intrastrand pyrimidine dimers (CPD dimers) only account for the less deadly, non-melanoma skin cancers (BCC, SCC). The goal of this project is to identify and characterize novel UV-induced DNA lesions that may serve as new signature mutations for melanoma, in the hope that we may suggest new diagnostic tools for life-saving early detection and that new insights on melanoma pathogenesis may lead to more effective therapeutic interventions. This project aims (1) to first screen for and identify new UV induced lesions, especially the more genotoxic interstrand DNA lesions in order to provide significant insights for a causative link between UV radiation and melanoma; and (2) to characterize these novel lesions and their repair kinetics in order to identify new UV-signature mutations for illuminating molecular mechanisms behind melanoma pathogenesis. To pursue the first aim, we will use HPLC-MS/MS technology to identify UV- induced DNA adducts in various mouse models of pigmentation. We will use phosphate tagging and oligonucleotides to determine inter- versus intrastrand nature of adducts, rule out known intrastrand photoproducts (heretofore linked to SCC and BCC), and focus especially on interstrand adducts, as they have never been reported in vivo before and as they are generally more genotoxic. Preliminary experiments have revealed the existence of such damaging adducts in a dosage-dependent and wavelength-dependent response. To pursue the second aim, we will use organic synthesis to validate our hypothesized structures; with well-developed structure hypotheses, we can better develop diagnostic tools for studying novel adducts. Together with flow-cytometry-based studies of repair kinetics and modified shuttle vector mutagenesis assays, we can identify the signature mutations of these novel UV-induced adducts, which (as suggested by preliminary analyses) can be aligned to genomic mutation patterns from melanoma databanks, thus helping us understand UV-induced melanoma pathogenesis.